<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Check Polygon</title>
  <style>
    #hint {
      position: absolute;
      left: 0;
      top: 0;
      width: 16px;
      height: 16px;
      line-height: 12px;
      text-align: center;
      transform: translate(-50%, -50%);
      display: none;
      border-radius: 50%;
      background-color: rgba(0, 0, 0, 0.4);
      color: white;
    }
    #hint.show {
      display: inline-block;
    }
  </style>
</head>
<body>
  <canvas id="gl-canvas" width="512" height="512"></canvas>
  <div id="hint">+</div>
  <div>
    在画布中点击鼠标绘制图形 <button id="clear">清除</button>
  </div>
  <script src="/check_polygon/app.js"></script>
</body>
</html>